Evaluation of surface roughness and wall thickness in the incremental stamping process with variation in the degrees of freedom of the contact tool

In this study, the performance of a rotating semi-spherical tool (with two degrees of freedom) is compared with another rigid semi-spherical tool, both with a diameter of 8.0 mm. The stamping is performed on AA1100 aluminium blanks with a thickness of 0.8 mm, using a helical strategy and single point incremental forming technique, with a feed rate of 1000 mm/min, a step depth of 0.1 mm, without rotation on the machine spindle and petroleum jelly as a lubricant. The behaviour of Ra and Rq roughness and wall thickness is evaluated during the tests. Scanning electron microscopy and dispersive energy spectroscopy are used to observe the wear mechanisms on the surface of the samples. On this basis, the tools for incremental stamping must promote continuous contact with the blank without generating excessive friction. Our results show that the rigid tool presents the best working conditions for the AA1100 aluminium sheets because it generates less roughness in the stamped parts, when compared with the rotating tool (~ 54% lower in the final average of the Ra roughness). The scanning electron microscopy image reveals the presence of adhesion both on the contact tip of the rotational tool and on the rigid tool, showing that the adhesive wear mechanism is predominant in the single point incremental forming process and influences the final roughness of the stamping cones.

A research on a new structure of forming tool in Single Point Incremental Forming (SPIF)

Single Point Incremental Forming (SPIF) is really a new technology of forming metal sheet nowadays and in recent decades. Although it was invented in, 1967 by Lezak, an American inventor, but the applications of the innovative technology were broad from 1990 because of the advance of controlling technology. This technology is especially adapted to small batch, unique or single productions. There are many forming parameters that influence to the formability of the metal sheet workpiece such as diameter of tool, the revolution per minute of the tool tip, the vertical feed rate after each orbit, the velocity of tool in horizontal plane…. Among of them, in our own experiences, we recognize that in almost all cases, the revolution per minute of the forming tool when forming ferric material sheet such as mild steel, stainless steel, hard steels… should be as small as possible to get the biggest ability of deformation of the workpiece sheet to get rid of failure on the lateral edge of the sheet. The tangential velocity of forming point on the spherical tool tip should be selected to attain the situation of rolling but no sliding of the surface of the spherical tool on the one of the sheet material. The paper recommends a new version of a forming tool in which the tip of the tool is a very hard ball (such as the quenched ball in a ball bearing) that is freely rotate by the friction to modify the contact point on the spherical surface of the tool to avoid the abrading and keep the spherical shape and the situation of rotating but no sliding on the surface of the workpiece sheet as mentioned above. The manufacture of the innovative forming tool is performed and then empirical processes verified it. The models formed by the typical tool are better in comparison with the ones of normal forming tool.

Incremental Forming of Sandwich Materials

In the last decade, a completely new process has been developed using the existing knowledge in machining and in flow forming and spinning processes, so called the Incremental Sheet Forming. In the process, a spherical tool, governed by CNC incrementally forms a sheet metal to form complex and asymmetric parts using minimum tooling. Several works have been published to study the process limits, optimization of paths for the forming of deep walls and to extent the formability of some alloys using temperature as a process variable. Few studies have been also published where the incremental forming of polymers has been studied. In this work, the forming of steel-polymer-steel hybrid material or Laminate Vibration Damping Steels (LVDS) is considered. Spinnability tests are used to study the process limits and the effects of having two independent sheets in the thickness of the initial blank. The maximum forming angle, forming vertical force and maximum strains near the fracture are presented for the sandwich material in comparison to steel with three different thicknesses and same composition.

A Study for the Mirror Surface Polishing by Using the Ring Shaped Tool

The feasibility of mirror surface polishing by using the ring shaped tool (abbreviated as the RST) is studied. This novel polishing process is expected to apply in the fabrication of precise mold and optics. In order to reduce the tool wear effect, the semi-spherical tool was replaced by the ring shaped tool. The experimental results show that the machining rate is not affected by the tool wear, That is, this new process provides excellent machining repeatability. On the other hand, the mirror surface with Ra 4.4nm was yielded in the lager area polishing.